Spin splitting in narrow InAs quantum wells with $In0.75Ga0.25As$ barrier layers

Using two independent magnetotransport experiments, i.e., thermal activation and the coincidence method in tilted fields, we determine the $g$ factor in a two-dimensional electron system in a 4-nm-wide InAs quantum well. From these independent techniques we deduce consistently an absolute value $|gexp|≅6.$ This is considerably smaller if compared to $|g|=14.8$ for bulk InAs. Nonparabolicity in InAs cannot fully explain the reduced $g$ factor. We argue that the penetration of the wave function into the $In0.75Ga0.25As$ barriers and into the $In0.75Al0.25As$ spacer layer plays an additional role.